As described in the prior work referred to above, systems in which the assembly can be opened out into a planar array of the tubes allow the assembly to be rolled after extrusion and thus conveniently transported to a site at which the assembly is to be installed, generally in a subterranean application.
At the site, the tubes of the assembly can be rolled together lengthwise to form a compact bundle which may be laid directly in the ground or can be fed into a protective pipe.
The cables can then be threaded through the tubes or conduits of the assembly. The planar assembly is generally formed from the thermoplastic synthetic resin by extrusion and can be rolled up immediately following extrusion for transport in the manner described.
It will be understood that the bundle formed by the tubes or conduits can be fixed in position, e.g. by wrapping a tie around the bundle or by equipping the bundle with appropriate means or retainers for holding the tubes in position.
The bundle can be laid straight or along an arcuate path and for that purpose and, to enable the coiling of the planar array on a drum and the uncoiling thereof, the assembly should be sufficiently elastically deformable to preclude collapse of the tubes and to enable the assembly to maintain its configuration both upon transportation and in the handling incident to bundling or opening up of the bundle.
Prior to the developments described in my earlier work, i.e. in the art, cable-guide conduits have been known wherein the individual plastic tubes have a round outer cross section and a correspondingly round inner cross section. This configuration facilitates fabrication as well as the coiling of the product on a drum and its uncoiling from the drum. When the tubes are, however, brought together in the bundle, they do not lie complementarily against one another, but rather have only line contact with one another.
As a consequence, between the plastic tubes and their webs, relatively large gaps and more or less free space can form. While this free space does facilitate arcuate placing of the cable-guide conduit bundle and relatively small radii of curvature, when the bundle is placed directly in the ground water can penetrate through the gaps and into the free spaces so that the cable-guide conduit bundle can become a drainage pipe along which water may run.
Soil and other materials in the environs of the bundle can penetrate into the gaps and free space and reduce the relative mobility of the conduits of the bundle in subterranean applications were some mobility is essential if rupture is to be precluded because of subsidence.
More recently, it has been proposed (see German Patent Document DE 36 03 849) to provide a cable-guide tube bundle which is composed of a plurality of plastic pipes which have a modified triangular outer cross section shape. The modified triangular shape has very pronounced rounding of the corners of the triangle and an outer limb which itself can be curved.
Because of this particular shape, within the interior of the bundle a relatively large amount of dead space is provided through which cable cannot be passed. The amount of material constituting the conduit bundle is comparatively high because the ratio of the cross section of the materials of the bundle to the ratio of the cross section of the cable passages is high.
Problems are also encountered with this system in the coiling of the extruded product because the shapes of the tubes provides a significant resistance to the coiling operation. Furthermore, in the coiling and uncoiling undesirable modifications of the cross section of the tubes may occur. Because of such deformations and deformations which occur in the placing of the tube bundle or shifting of the earth in which the tube bundles are received, rupture can occur between the individual plastic tubes so that water can penetrate into the assembly.
In German Patent Document DE 39 09 813 (see U.S. Pat. No. 5,036,891), I have described a conduit assembly which can be coiled and uncoiled without difficulty. Detrimental free spaces are not of concern. In that system the plastic tubes have polygonal outer cross sections with more than three sides so that, in the bundled configuration, the individual plastic tubes fit complementarily together. The plastic tubes can, however, be unbundled to a planar array for coiling and uncoiling. In a preferred embodiment, the individual plastic tubes have hexagonal cross sections.
The cable-guide assembly there described satisfies all of the requirements for handling and in placing in the ground, but in regions subject to shifting of the ground, earthquake regions or regions in which there is substantial subsidence, the stability of the tube bundle can be improved further.